New techniques and processes for manufacturing semiconductor devices have created new challenges for maintaining and operating the machines in which semiconductor devices are made.
The manufacture of semiconductor devices, such as microprocessors and memory chips, is primarily carried out by chemical processes. Machines called reactor chambers implement these processes, the most common of which is a process known as chemical vapor deposition (CVD). CVD, as the name implies, is a chemical process that allows a manufacturer to deposit, or grow, layers of material onto the surface of a substrate, such as a silicon wafer. To carry out the CVD process, the reactor chamber will create an environment around the substrate of selected process conditions. Typically this involves controlling the temperature and pressure within the chamber. A gas delivery system introduces reactant materials into the chamber. By maintaining the proper environment and by introducing the proper materials, the CVD reaction will occur and the gaseous reactant materials will form, or deposit, a solid phase material onto the surface of the substrate. Each layer of solid phase material is formed into a pattern, typically by photolithography, or by an etching process. By depositing multiple layers of different patterns onto the substrate, a complete semiconductor device can be formed.
As one might expect, these chemical processes can lead to the build up of solid material on the walls and components of the reactor chamber. Over time, these deposits accumulate and eventually form a thick film of byproduct, or waste, material that coats the inside of the chamber. This film of material becomes a source of particulate matter that is harmful to the formation of a semiconductor device. Specifically, it is known that this film can flake off the reactor walls during thermal expansion and contraction of the processing equipment, and in some cases due to reactions with moisture. The flaked-off byproduct can contaminate the substrates being processed within the chamber and prevent the deposition of device quality films.
Contaminants can be removed from the walls of the chamber and the reactor components by opening the chamber and cleaning manually the chamber walls with a liquid solvent, much like the interior of an oven is cleaned. Although this process can work, the procedure is labor intensive and time consuming as a high degree of cleanliness is required.
To provide a better solution, alternative cleaning procedures have been developed including in-situ cleaning processes during which gaseous agents are fed into the chamber and reacted with the byproduct material to cause the byproduct material to dissolve into the agent and exhaust from the chamber. In some of these processes, the reagent is fed into the chamber and a plasma is struck. The plasma is understood to assist in the break-up of reagent molecules and to provide reactive etch ions for the cleaning process. Several such plasma-assisted processes are known, including processes based on NF.sub.3, SF.sub.6 and C.sub.2 F.sub.4 reagents.
Chlorine trifluoride (ClF.sub.3) is a cleaning agent that can clean reactor walls even in the absence of a plasma. ClF.sub.3 is a weakly bound molecule that dissociates exothermically on contact with most hot metal surfaces. The energy released from this exothermic reaction is used to volatize the reaction byproduct which can then be pumped out of the chamber and to an appropriate abatement station leaving the reactor surfaces clean. The plasma-independent capability of the ClF.sub.3 cleaning agent gives it a major advantage over other cleaning agents. For example, ClF.sub.3 reacts with and cleans surfaces that are not accessible to a plasma, such as reactor walls, the backside of a heater stage and even exhaust lines.
However, new metal CVD technologies create byproducts that challenge the existing techniques of in-situ cleaning. In particular, many new metalization techniques employ halogen based precursor gases that give rise to residual films that are rich in halogen as well as metal. These films have proven more resistant to existing cleaning techniques than the silicon based films produced during silicon deposition. This leaves unclean surfaces that can contaminate the wafers being processed. Longer cleaning times have been proposed as a solution, but the results achieved have been mixed and the delay incurred adds to the expense of operating the semiconductor production equipment, and increases cleaning costs by increasing the use of ClF.sub.3, a relatively expensive reagent.
Accordingly, there is a need in the art to provide improved cleaning techniques, including techniques more suited to removing films created during metal CVD processes.